A creatinine muscle index (CMI) demonstrated superior mortality prediction compared to conventional sarcopenia markers in 2,981 chronic kidney disease patients followed for median 4.1 years. The CMI, calculated from serum creatinine divided by cystatin C, showed stronger associations with death risk across all CKD stages than established eGFR ratio methods or difference calculations. This represents a meaningful advance in CKD care, where muscle wasting affects up to 60% of patients but remains difficult to detect clinically. Unlike imaging-based assessments or physical performance tests, CMI requires only routine blood markers already collected in CKD monitoring, making it immediately implementable in clinical practice. The finding addresses a critical gap since sarcopenia in CKD patients carries particularly high mortality risk due to the intersection of uremic toxins, chronic inflammation, and metabolic acidosis that accelerate muscle catabolism. Previous creatinine-cystatin C indices showed inconsistent performance in kidney disease populations, likely due to altered creatinine handling. However, this study's larger CKD-specific cohort and longer follow-up period provide more definitive evidence for CMI's clinical utility. The simplicity of incorporating CMI into existing laboratory workflows could enable earlier identification of high-risk patients for targeted interventions, potentially improving outcomes in this vulnerable population.